FIELD OF THE INVENTION
In the printing industry, and particularly in a printing process, a continuous web of paper is first passed through the printing press which makes the ink impressions on the web. The moving web is then immediately passed through an oven to remove solvents and wetting solution retained from the printing process. The web is then cooled down by passing it over chill rollers. At this point the web is then ready to be folded and cut into its final format.
The present invention relates to an improved system for cutting a continuous paper web into separate sheets or signatures, alternately diverting or separating the individual sheets into two paths to create a space or gap between successive sheets and then decelerating and shingling or overlapping the successive sheets for delivery of the sheets to a subsequent process such as a sheet counter or stacker system as described in my U.S. Pat. No. 4,652,197. The present invention operates equally well with signatures which are one sheet thick or with signatures which are several sheets thick such as pamphlets, magazines or newspapers.
It is desirable to provide a diverter and delivery system in which sheets cut from the continuous web are alternately diverted into separate delivery paths by an improved diverter means. Additionally, it is desirable to provide an improved diverter and delivery system which maintains continuous, positive control over the sheets while the sheets are first cut and alternately diverted and then shingled in preparation for delivery to a subsequent processing station. Moreover, it is desirable to provide an improved delivery system which operates at a dramatically increased speed with respect to present delivery systems. The cutting operation, described in connection with the preferred embodiment of the present invention, is fully set forth in and described in my U.S. Pat. No. 4,426,897.
Previous diverting systems employ various methods and devices for directing sheets. The prior art discloses fixed or static diverters; cutting cylinders which additionally function as diverters; and rotating cam diverters.
Fixed or static diverters are disposed across the paper path and these diverters operate by having the sheets physically strike the diverter. The momentum of the moving sheets and the shape of the diverter surface combine to channel the sheets to the appropriate delivery conveyor. Such fixed diverter systems create the possibility of a lead edge foul condition as the lead edge of each sheet hits the diverter; generate static in the sheets as the sheets move across the stationary surface of the diverter; and are not variable in width to adapt to paper of differing widths. Each of these problems can ultimately jam the system thereby losing valuable time while the jam is cleared, wasting large amounts of paper in getting the system back up to running speed, and potentially damaging the machine itself. Lead edge foul is even more probable with a signature of more than one sheet when the leading edge is open. Due to the speed of travel of the signature, the leading edges of the group of sheets may separate thereby presenting a ripe target for causing a jam with the forward edge of the fixed diverter.
The problems associated with static diverters multiply when single sheets or signatures comprised of a few lightweight sheets are involved rather than a folded signature. Single or thin bundles of sheets, when unfolded, have less structural rigidity and are more apt to buckle when striking the fixed diverter. With folded signatures, a rigid spine is created by the fold which aids in maintaining structural integrity of the sheets as they strike and slide across the diverter. Moreover, the static generated from sheets sliding across the surface of the diverter is more likely to stop or misalign a single sheet of paper, because of its lighter weight, than a bundle of sheets.
In other prior art systems the cutting operation can perform the dual function of cutting the web of paper and then alternately diverting the individual sheets. In such systems, the web is passed between two, opposed knife cylinders, each of which includes a knife edge that is 180.degree. out of phase with the knife edge of the other cylinder. These knife cylinders further include a row of cam operated pins which pierce and grip the web and then deliver the cut sheet to an associated delivery cylinder. Each delivery cylinder includes a cam operated gripper that grabs the leading edge of the cut sheet as the pins in the knife cylinder are withdrawn and deposits the cut sheets in a shingled fashion on a delivery conveyor system. As each successive sheet is layed down in a shingled format on the respective delivery conveyors, the gripper of the delivery cylinder releases the sheet. However, operations such as these create a great deal of wasted paper because the sheet edges must be subsequently cut in order to remove the pin holes. Moreover, the need to cut the edges adds a further processing step to the overall system which increases the time to produce a finished product and increases the costs.
Still further prior art systems disclose rotary cam diverters for alternately diverting successive sheets between two delivery systems. An example is shown in the British Pat. No. 1,208,969. However, the system disclosed therein, because of its construction, creates potential jamming problems. Specifically, as the lower cams divert a sheet to the upper delivery system, the placement of the cams combined with the physical contour of the cams cause the cams to lose contact with the leading edge of the sheet prior to the sheet becoming trapped between the opposed belts of the upper delivery system. This lack of support can cause the leading edge of the sheet to drop and miss the entry into the delivery system. As a result, the sheet would foul and jam the system. Additionally, the static associated with the overlying belt against which the cams trap the sheet would actually repel a single or lightweight sheet prior to the leading edge being engaged by the upper and lower opposed belts of the delivery system. Consequently, the same fouling or jamming would occur.
In an attempt to remedy these problems, the prior art further shows the addition of guide members or steeples, as are shown in U.S. Pat. No. 4,373,713, which act in combination with the cams to provide continued support for the sheets while they are diverted to the delivery conveyors. While solving the support problem these guide plates create still greater static problems. As with a fixed diverter, the sheets are required to slide across the guide member which action creates static electricity. The generated static is sufficient to impede and misalign, if not jam, single or lightweight sheets. Consequently, the system disclosed is not only limited in the number, type and weight of sheets it can run but, more importantly, the system creates additional problems which it does not solve.
Various delivery systems, for shingling sheets are also set forth in the prior art. With delivery systems generally, it has always been a goal to increase the overall operating speed of the system. While printing presses operate at high speeds, it has always been necessary to drastically reduce the speed of the sheets in the delivery system both to shingle and to square the sheets. Squaring the sheets may be achieved by allowing the lead edge of each sheet to strike a fixed object such as a squaring roller. However, to avoid permanent damage to the sheets, particularly single or lightweight sheets, the paper should not be travelling faster than about 300 feet per minute. This limitation is a physical characteristic of most normal weight paper and, consequently, limits the overall output of the printing system by necessitating a reduced operating speed for the delivery system.
One delivery means known in the art is described above in connection with the rotary knife cylinders and cam operated pin grippers. This system employs a pair of delivery cylinders which grip alternate sheets and deposit them in overlapping relation on separate delivery conveyors. However, the need to cut off the edges of the sheets to remove the pin holes creates an additional handling step which makes this system slow and inefficient.
Another prior art delivery system employs a fan like element to shingle the sheets. By means of gravity, sheets are caused to fall into a receptive slot in a rotating fan-like delivery means. As the delivery means rotates the sheets fall out one after the other in an overlying or shingled arrangement. However, once a sheet has entered the fan delivery, the timing of the entire delivery system is subject to the gravitational forces working on the sheet. As a result, lightweight sheets could severely slow down a system otherwise capable of operating at higher speeds. The delivery system of the present invention improves upon this arrangement by maintaining continuous and positive control of each and every sheet, which this prior art system cannot do, and by increasing the operating speed with respect to this prior art system.
Other prior art delivery systems employ rotary knock down arms for decelerating the sheets but still require squaring rollers for aligning the sheets. While the knock down arms, by acting on the tail of the sheets, are an improvement over the use of fixed stops in decelerating the sheets, critical speed limitations are still present because of the squaring roller. Moreover, the knock down arm merely strikes the rapidly moving sheet throwing the sheet against a lower, slow speed belt. Because the sheet is unrestrained at this time the chance of it becoming misaligned or out of square is great.
An improvement over that system is disclosed in my U.S. Pat. No. 3,994,221. While still using a squaring roller, the deceleration procedure is improved by the use of a series of freely rotating snubber wheels mounted on rotating snubber support plates. Instead of only knocking the sheet down, allowing it to bounce onto the lower, slow speed belt, the snubber wheels actually physically trap the tails of the sheets against the slow speed belt while the lead edges of the sheets engage the squaring roller. This causes the sheets to decelerate more quickly but can still allow a misalignment. Consequently a squaring roller is still needed and still places a speed limitation on the system.
The present invention overcomes all of the aforementioned problems by maintaining a positive control over the sheets exiting the opposed, high-speed belts, during the decelerating process of the snubbers and during subsequent delivery. Specifically, the snubber wheels trap the individual sheets against the lower, slow speed belts while the tail of the sheets are still engaged by the opposed high-speed belts or immediately after the sheet has left the high-speed belts. While this may create a slight overfeed of the tail end of the sheets, it is not significant enough to permanently crease the sheets. By maintaining this positive control, the sheets are never allowed to become unaligned. Thus, the continual positive control allows the removal of the squaring roller which, in turn, allows the system to operate at a faster speed.